1

在 Java 中，我得到一个强制转换异常：

java.lang.ClassCastException: java.util.concurrent.ThreadPoolExecutor$Worker
incompatible with com.myco.TaskListEntry
at com.myco.JobThreadFactory.newThread(JobThreadFactory.java:17)

这是代码：

public class JobThreadFactory implements ThreadFactory {
    @Override
    public Thread newThread(Runnable r) {
        TaskListEntry entry = (TaskListEntry)r;   //<== Cast exception!
        return new Thread(r, "Thread for " + entry.toString());
    }
}

@DisallowConcurrentExecution
public class WorksheetSessionJob implements Job {
    private List<TaskListEntry> taskListEntries;

    @Override
    public void execute(JobExecutionContext jobContext) throws JobExecutionException {
        ThreadFactory threadFactory = new JobThreadFactory();
        ExecutorService executor = Executors.newCachedThreadPool(threadFactory);
        for( TaskListEntry nextEntry : getWorkListEntries() ) {
            executor.execute(nextEntry);
        }
    }

    private List<TaskListEntry> getWorkListEntries() {
        List<TaskListEntry> entries = new ArrayList<TaskListEntry>();

        // TODO Get rows from DB - for now, make something up to test with
        //-- beginning of fake data creation ----------
        TaskListEntry entry = new TaskListEntry("0022", "04590150560", "DI_MODULAR", 1);
        entries.add(entry);
        entry = new TaskListEntry("0007", "04590150560", "DI_MODULAR", 2);
        entries.add(entry);
        //-- end of fake data creation ----------------

        return entries;
    }

}

public class TaskListEntry implements Runnable {
    private String  worksheetNumber;
    private String  specimenNumber;
    private String  instrumentName;
    private int     id;

    public TaskListEntry(String worksheetNumber, 
            String specimenNumber, String instrumentName, int id) {
        super();
        this.worksheetNumber = worksheetNumber;
        this.specimenNumber = specimenNumber;
        this.instrumentName = instrumentName;
        this.id = id;
    }

    @Override
    synchronized public void run() {
        // executor in my Job should have created a thread for me to run in
        //-- TESTING ONLY -------------
        try {
            Thread.sleep(10000);    //force execution to another thread?
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //-- END OF TESTING -----------
    }

}

为什么没有发送我的 TaskListEntry 可运行文件？我需要使用该类中的值来命名相应的线程。我究竟做错了什么？！

4

1 回答 1

4

您遇到了演员问题，因为当调用线程工厂时，您Runnable与ThreadPoolExecutor$Worker该类无关。这Worker Runnable是一个内部执行器类，它从BlockingQueue保存您的TaskListEntry实例的内部中取出任务。您的任务无法通过设计与特定线程相关联。如果您将 100k 任务提交到队列中，您不会希望它产生 100k 线程——这就是使用线程池的全部意义所在。

If you are trying to somehow track which threads are processing which tasks, I would suggest logging the thread-id (Thread.currentThread().getId()) inside of the TaskListEntry.run() method. But if you are trying to see each task somehow in the thread-names, you aren't understanding how the thread-pool works. Typically, I use a ThreadFactory to set the name on pool threads to identify the pool name. Something like "TaskListEntry pool-1" or something would be an appropriate thread-name here.

If you explain more about what you are trying to accomplish with regards to the names, we may be able to provide more help.

于 2013-02-27T22:13:59.617 回答